Particular embodiments generally relate to switching circuits, and in a particular example, to class D amplifier supply circuits and methods.
Portable devices require more efficient circuits to extend battery power for longer periods of time. Cellular phones and personal digital assistants (PDAs) use low voltage and switching control circuits to improve power efficiency. Portable devices may use class D amplifiers that use switching to efficiently generate music and voice.
FIG. 1 illustrates a conventional single ended class D amplifier system 100. System 100 includes a class D amplifier 101 that receives an input and generates a switching signal at a node A. Class D amplifier 101 produces the switching signal at point A by switching between the voltage rails (e.g., Vdd and ground). This switching signal may be filtered by a filter 102 (e.g., an inductor 106 and a capacitor 108) to produce a power signal at the output node appropriate for driving a speaker 104.
Some applications require the single ended class D amplifier configuration, as shown in FIG. 1, to generate audio using a single battery 105 (e.g., lithium ion battery) having a voltage Vdd. The nominal output voltage of class D amplifier 101 will be between the supply voltage Vdd and ground and requires a large direct current (DC) coupling capacitor 103 at an output node. DC coupling capacitor 103 may degrade the low frequency response of class D amplifier system 100. Also, capacitor 103 may be very large and may increase the footprint of a portable application.
Some applications may use complimentary supplies so that an output capacitor is not needed. However, additional supplies require additional circuitry incorporating a great deal of active devices that may consume more power and use more space. These circuits may also be designed for a specific voltage and restrict flexibility in application design.